Signal translating stage



Nov. 25, 1941 A. I. LOUGHREN 2,263,825

SIGNAL TRANSLATING STAGE Filed May 15, 1940 2 Sheets-Sheet 2 FIG.6.

Grid Voltage Grid Volta'ge i INVENTOR ARTHUR V. LOUGHREN ATTORNEYPatented Nov. 25, 1941 UHTED SIGNAL TRANSLATING STAGE Arthur V.Loughren, Great Neck, N. Y., assignor to Hazeltine Corporatio ware n, a.corporation or Dela- Application May 15, 1940, Serial No. 335,238

(Cl. 250-20) l 1'7 Claims.

This invention relates generally to signaltranslating stages for thetranslation of signals within a wide amplitude range and particularly tosuch stages in which the gain is controlled inversely in accordance withthe amplitude of the signal input to the stage.

Under normal operating conditions, a modulated-carrier signal receiveris utilized for the reception of signals of amplitudes varying withinvery wide limits. As a result, the signal input to the first repeaterstage of the receiver normally has a correspondingly wide range ofamplitude variations. For weak signals, it is desirable to maintain thetransmission characteristics or the response of the preselector betweenthe antenna and the first repeater stage of the receiver at a maximum inorder to raise the received signals substantially above the noise level,

thus to procure maximum useful sensitivity of the receiver. However,with a high gain in the preselector, as the strength of desired receivedsignals increases to such an extent that the grid swing of the firstrepeater stage includes a substantial nonlinear portion of thecharacteristic curve of the repeater, distortion of the desiredsignal-modulation envelope and cross modulation of the desiredsignal-carrier wave by strong undesired signals may result. This isparticularly true in the case of receivers provided with automaticamplification control by which strong signals cause the grid of thefirst repeater stage to be biased toward that portion of itscharacteristic which is most nonlinear. The undesired signals, as wellas desired signals, which reach the grid of the first repeater stage 01the receiver have the .efiect of causing the grid to swing over such arange that these disturbing effects result. It is well known that suchenvelope distortion and cross modulation are efiects which cannot befiltered out by succeeding selective circuits of the receiver.

In general, the preselector of a receiver, that is, the selector circuitbetween the antenna and the input circuit of the first vacuum-tuberemore, this does not remove the envelope distortion of abnormallystrong desired signals.

Various expedients have heretofore been proposed for automatically andadjustably attenuating the input to the first repeater stage or amodulated-carrier receiver in order to eliminate the disturbing effectsdescribed above. In certain of these arrangements, adjustable impedanceelements such as vacuum tubes have been connected in circuit with'thepreselector circuit oi the receiver adjustably to damp such circuit,thereby adjustably to attenuate the signal input to the first repeaterstage. Other proposed arrangements for this purpose comprise twofeed-forward coupling paths between the antenna and the firstvacuum-tube repeater of the signal-translating channel so arranged as toapply signal voltages of opposite phase to the input circuit of thefirst repeater, the transmission characteristics of one of the couplingpaths being adjustable. While such arrangements provide generallysatisfactory operation, they have generally required the use of one ormore additional vacuum tubes or other circuit complexities that tendedto increase the cost oi. the receiver.

It is an object 01' the invention, therefore, effectively to provide animproved, simple, and economical signal-translating stage which may .beeasily adjusted to control the sensitivity or a modulated-carrier signalreceiver in such manner as to eliminate the undesired effects describedabove.

It' is another object of the invention effectively to provide asignal-translating stage which secures the desired characteristicsdescribed without affecting the selectivity of a radio-frequencyselector with which it is associated.

It is still another object of the invention to provide asignal-translating stage: adapted for 40 the translation or a signalinput which varies tion eilects.

pea-ter in the signal-translating channel, should be selective to pass aband of desired modulation frequencies sufiiciently wide to provide thedesired fidelity of reproduction. Generally speaking, if an attempt ismade to decrease the total desired and undesired signal input of thefirst repeater stage by discriminating against the un- In accordancewith the invention, a signaltranslating stage comprises a vacuum tubeincluding a source of electrons, an anode, a control electrode, and asignal-input electrode between said control electrode and said anodeetdesired signals passed by the selector by adjusting its band width,the fidelity of reproduction fective to control the electron stream fromthe source to the anode and having a greater effect on the electronstream over one cross-sectional portion of the electron path than onthat over is impaired to an undesirable degree. Furtheranother portionso that, normally, the transconductance from the control electrode tothe anode is primarily determined by the control of ace-spas derived.The audio-frequency signals are, in turn, amplified by theaudio-frequency amplifier i8 and supplied to sound reproducer I! forreproduction. The automatic amplification control bias derived from unitI! is effective to maintain the signal input to detector 15 withinrelatively narrow limits for a wide range of received signalintensities.

Referring now-more particularly to the signaltranslating stage i2 of theinvention, this stage comprises a vacuum tube including, in the ordernamed, a source of electrons such as a cathode ii, a first or controlelectrode 22, a second electrode 22, a third or signal-input electrode24, a screen electrode 25, and an anode 26. The

' signal-input electrode 24 is effective primarily to For a betterunderstanding of the invention, together with other and further objectsthereof,

reference is had to the following description taken in connection withthe accompanying drawingaand its scope will be pointed out in theappended claims.

Referring now to the drawings, Fig. 1 is a ditcuit diagram, partlyschematic, of a modulatedcarrier signal receiver of the superheterodynetype including a signal-translatingstage in accordance with theinvention; Figs. 2' and 3 are circuit diagrams of modifications of thesignal-- translating stage of Fig. 1; Fig. i ls a circuit diagram.partly schematic, of a receiver of the su-' perheterodyne type includinga signal-translatcontrol the variations in electron stream from cathode2i to anode 26 at signal-input frequen cies and is so designed aseffectively to extend ing stage in'accordance with the invention andFigs. 6 and 'l comprise graphs utilized to explain the operation of thecircuit of Fig. 1.

Referring now particularly to Fig. 1 of the drawings, there is shown acircuit diagram, partly schematic, of a complete modulated-carriersignal receiver of the superheterodyne type employing the invention.This receiver comprises, coupled in cascade with an antenna-groundcircuit I0, I I, a radio-frequency amplifier I2, a frequency changer oroscillator-modulator i3, an intermediate-frequency amplifier i4 of oneor more stages, a detector and automatic amplification control or A. V.C. supply IS, an audio-frequency amplifier it of one or more stages, anda sound reproducer .11. Automatic amplification control is secured in awell-known manner by applying a unidirectional voltage derived from theA. V. C. supply 15 to the control electrodes of oscillatormodulator i3and one or more of the tubes included in the intermediate-frequencyamplifier l4. Automatic amplificationcontrol potentials are also appliedto radio-frequency amplifier If in a manner to be hereinafter fullydescribed.

Neglecting for the present the details of operation ofsignal-translating stage i2. of the present invention, the apparatusdescribed constitutes, in general, a conventional superheterodynewave-signal receiver, the operation of which is well-understood in theart. In brief, signals intercepted by antenna-ground circuit l0, II aretranslated to the input circuit of radio-frequency amplifier l2, areamplified therein and translated to oscillator-modulator i3 wherein theyare converted to an intermediate-frequency signal. Theintermediate-frequency signal is amplified in intermediate-frequencyamplifier I4 and delivered to detector I! wherein the audio-frequencysignals and the A. V. ,C. biasing potentials are 75 the path directlythrough grid 24 is mainly etover only a portion of the cross-sectionalarea oi the electron path from cathode 2i to anode 24. An additional'orauxiliary electrode 21 is pro vided which extends over another portionof the cross-sectional area of the electron path between cathode 2i andanode 2| and is generally complementary to the signal-input electrode24. Electrode 24 is loosely coupled to electrode 21 by means ofcapacitance 8i shown in dotted lines for the reason that it may becomprised in whole or inpart or the interelectrode capacitance be--tween these electrodes. Electrode 21 is also designed so as to extendover only a portion of the entire cross-sectional area of the electronpath. Positive operating potentials are supplied to electrodes 23 and 25and anode 26 from suitable sources, while negative operating potentialsare supplied to electrodes 24 and 21, the operating potential applied toelectrode 21 being applied through an impedance 21'. A negative voltage,variable in accordance with the amplitude of received signals, isapplied to electrode 22 from the A. V. C. supply source ll.

in considering the operation of the signaltranslating stage of Fig. 1,it will be seen that signal-input electrode 24 has more effect on oneportion, which may be called portion A, of the cross-sectional area ofth cathode-anode electron path than on another portion, that is, theportion over which electrode 21 extends, which may be called portion B,so that, normally, that is, in the absence of an appreciable negativepotential applied to electrode 22 from the A. V. C.

fect the transconductance between electrode 24 and anode 28, but only toa relatively small degree, due to the action of electrode 21 on theportion B of the electron stream.

As the negative bias applied to electrode 22 is increased, due to anincreased signal-input amplitude and an increased A. V. C. bias, theratio of the density of the electron stream over portion B to that overportion A is increased, whereby the portion of the transconductancebetween sig- A. V. C. voltage applied to control electrode 22,

fective in determining the transconductance between signal-inputelectrode 24 and anode 26. As a larger A. V. C. bias is applied toelectrode 22, the transconductance of this path may be graduallydecreased to complete cutoff and the resultant transconductance fromsignal-input electrode 24 to anode is then only that due to the electronstream through grid 21. The means for applying the unidirectional A. V.C. control potential to control electrode 22 is thus efiective toincrease the average density of the electron stream over portion Brelative to that over portion A, whereby the portion of thetransconductance of the tube determined by the electron stream throughportion B is materially increased. Also, it is preferable that theelectrode structure of the tube is so related to its operating poten*tials that screen electrode 23, to which a positive potential isapplied,.is efiective, together with the the electron current to anode26 may be controlled by the signal voltages on electrodes 24 and 21.

Reference is made to the graphs of Figs. 8 and connected to cathode 2|.A resonant circuit 23,

84 is included in the anode circuit of tube 30. and it will beunderstood that the remainder of tron stream by virtue of itselectrostatic field which extends somewhat over the remainingpom tion ofthe electron path. Suppressor electrode 32 has the same purpose in thetube as the suppressor electrodes of conventional tubes,

which purpose iswell understood by those skilled in the art.

In Fig. 3, there is shown a signal-translating stage generally similarto that ofFig. 2 and circuit elements which are similar to those ofFigs.

1 and 2 have identical reference numerals. The

1 signal-translating stage of Fig. 3 comprises a 7 for a furtherexplanation of the operating characteristics of the signal-translatingstage II.

The curve A of Fig. 6 represents the grid voltage-anode currentcharacteristic of portion A of tube 20, while curve B represents thecorresponding characteristic for portion B. If an input signalof smallamplitude is applied to control electrode 24 or tube '20.'the resultantgrid voltage-anode current characteristic of the tube is thatrepresented by the sum of curves A and B,

which is represented by curve C. Thus, for a small signal input, asindicated by curve a, a relatively large signal output. as indicated bythe curve a, is obtained. Similarly, if the input signal is very large,as indicated by the c e b, the effective or over-all input voltage-outpucurrent characteristic of the tube is that of curve B and an outputsignal represented by the curve b is obtained from the stage. If now aninput signal of intermediate amplitude value is applied to thesignal-translating stage, it is seen that an A. V. C. bias is developedand applied to electrode 22 eflectively changing the transconductancecharacteristic of portion A of the tube and the changed characteristicmay be as represented by curve A of Fig. 7. The characteristic ofportion B is not materially changed, so that the over-all characteristicof the tube is that represented by the sum of curve A of Fig. 7 andcurve B of Fig. 6, which over-all characteristic is illustrated by thecurve D. Therefore, for an input erally similar to thesignal-translating stage i 2 of Fig. 1 and similar circuit elements haveidentical reference numerals. The tube 30 of Fig. 2 is generally similarto the tube of Fig.1 except that electrode 21 has been omitted and thereis included a suppressor electrode 32 disposed between screen grid 25and anode 26 and 43, by-passed for signal-frequency currents bycondenser 44, is provided for tube 40, electrode 4| being grounded.

In considering the operation of the signaltranslating stage of Fig. 3 itwill be.seen that,

for received signal amplitudes of. low value, for which maximum gain isrequired from tube 40,"

substantially .no current flows through grid 21 due to the effect ofnegatively biased electrode 4| and the electron stream through thesignalinput grid 24 is mainly effective to determine transconductancebetween control electrode 24 and anode 28.r As the amplitude of receivedsignals increases, the bias applied to electrode 22 from the A. V. C.source gradually increases. ultimately cutting oil the electron streamthrough control electrode 24. and reducing the negative bias on grid 4|so that an electron path is open through grid 4| to anode 28. That is,sufiicient bias voltage is developed-across resistor 43 to cut oil theelectron stream through grid 4| when a small A. V. C. 'bias is appliedto grid 22 and, as the A. ,V. C. bias to grid 22 increases, the biasvoltage developed in resistor 43 for grid 4i is decreased, therebypermitting the electron stream to flow through grid 4| and grid 21 in apath which is controlled to 'a much lesser'extent by the potential ofsignal-input electrode 24. '.It

is, therefore, seen that the transc'onductance of portion B of the tubeof Fig. 3 increases from a negligible value to some value as representedby the curve B of Fig. 6 while the transconductance of portion A of thetubes falls-from avalue as represented by curve A of Fig. 6 to acre.

. The signal receiver represented in Fig. 4 is generally similar to thatof Fig. 1 and similar circuit elements have identical referencenumerals. Thecircuit of Fig. 4 diflers from that of Fig. l primarily inthat it contains no stage of radio-frequency amplification, thesignal-translatmg stage of the invention being included in the circuitof the receiver as a converter stage ior developing anintermediate-frequency signal for intermediate-frequency. amplifier l4.signal-translating stage of Fig. 4 includes a vacuum tube 50 havingbetween screen electrode 21 and anode 26 an electrode supplied withoscillations from a conventional local oscillator 53. It is believedthat the operation of the circuit of Fig. 4 will be readily apparentfrom the description of the circuits of the preceding figures; that is,the action oi. grid 24 is generally similar and the oscillation voltagesupplied to grid 5| is also efiective to vary or modulate at thefrequency of local oscillator 53, the resultant electron stream to anode26. Therefore, for a received signal of low amplitude, the conversiontransconductance from signal-input electrode 24 aaoaaas electron streamover said other of said portions to that over said one or said portions,whereby the portion of said transconductance determined by the electronstream through said other of said portions is materially increased.

2. A signal-translating stage comprising, a vacuum tube including asource of electrons, an anode, a control electrode, and a signal-inputelectrode between said control electrode and said anode eflective tocontrol the electron stream from said source to said anode and extendingover only a portion 0! the cross-sectional area of the electron pathwhereby it has a greater eflect on the electron stream over said portionthan on that over another portion so thatnormally the transconductancefrom said signalto anode 26 is primarily determined by the electronstream through the grid-24. For strong signals, however, the conversiontransconductance from signal-input electrode 24 to anode 28 is primarilydetermined by the electron stream through grid 21, the potential appliedto signalinput electrode 24 having a lesser effect upon this portion ofthe electron stream.

The receiver of Fig. 5 is generally similar to that of Fig. 4 andsimilar circuit elements have identical reference numerals. The receiverof Fig. 5 differs from that of Fig. 4 in that the signal-translatingstage embodying the invention is an oscillator-modulator, there beingincluded in such signal-translating stage means for developing sustainedoscillations which are applied source of operating potential +B, thereis shown included in intermediate-frequency amplifier ll an anode loadimpedance for intermediate ire- 'quencies which comprises tuned circuit33, 3| to which is inductively coupled an inductanc 51. It will beunderstood that the remaining portions oi. intermediate-frequencyamplifier H which are not shown may be of conventional construction andoperation.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A signal-translating stage comprising, a vacuum tube including asource of electrons, an' anode, a control electrode, and a signal-inputelectrode between said control electrode and said anode efiective tocontrol the electron stream from said source to said anode and having agreater efiect on the electron stream over one cross-sectional portionof the electron path than on that over another portion so that normallythe transconductance from said signal-input electrode to said anode isprimarily determined by the control of the electron stream through saidone portion, and means for applying a unidirectional potential to saidcontrol electrode for increasing the ratio of the average density 01'the input electrode to said anode is primarily determined by the controlor the electron stream through said one portion, and means for applyinga unidirectional potential to said control electrode for increasing theratio of the average density of the electron stream over said other ofsaid portions to that over said one of said portions. where-' by theportion of said transconductance determined by the electron streamthrough said other of said portions is materially increased.

3. A signal-translating stage comprising, a

vacuum tube including a source of electrons, an anode, a controlelectrode, a signal-input electrode between said control electrode andsaid anode efiective to control the electron stream from said source tosaid anode and effectively extending over only a portion of thecross-sectional area oi. the electron path, whereby it has a greatereffect on the electron stream over one cross-sectional portion of theelectron path than on that over another portion, an auxiliarysignalinput electrode effective to control the electron stream from saidsource to said anode extending over said other portion and normallybeing less effective than said signal-input electrode so that normallythe transconductance from said signalinput electrode to said anode isprimarily determinedby the control of the electron stream through saidone portion, and means for applying a-unidirectional potential to saidcontrol electrode for increasing the ratio of the average density oi.the electron stream over said other of said portions to that over saidone of said portions, whereby the portion of said transconductancedetermined by the stream through said other of said portions ismaterially increased.

4. A signal-translating stage comprising, a vacuum tube including asource of electrons, an anode, a signal-input electrode eil'ective tocontrol the electron stream from said source to said anode efi'ectivelyextending over only a portion of the cross-sectional area of theelectron path. whereby it has a greater eflect on the electron streamover one cross-sectional portion of the, electron path than on that overanother portion, an auxiliary control electrode effective to control theelectron stream from said source to said anode extending over said otherportion so that normally the transconductance from said signalinputelectrode to said anode is primarily determined by the control of theelectron stream through said one portion, means for applying a signalinput to said signal-input electrode and for applying a small fractionof said signal input to said auxiliary electrode, and means forincreasing the ratio of the average density of the electron stream oversaid other of said portions by the stream through said other of saidportions is materially increased.

5. A signal-translating stage comprising, a vacuum tube including asource of electrons,'an anode, a control electrode, a signal-inputelectrode between said control electrode and said anode effective tocontrol the electron stream from said source to said anode and having agreater effect on the electron stream over one cross-sectional portionof the electron path than on that over another portion, and an auxiliarycontrol electrode effective to control the electron stream from saidsource to said anode and having a greater effect on said other portionthan on said one portion, said stage including means loosely couplingsaid signal-input electrode and said additional control electrode sothat normally the, transconductance between said signal-input electrodeand said anode is primarily determined by the control of the electronstream through said one portion, and means for applying a unidirectionalpotential to said control electrode for increasing the ratio of theaverage density of the electron stream over said other of said portionsto that over said one of said portions, whereby the portion of saidtransconductance determined by the electron stream through said other ofsaid portions is materially increased.

6. A signal-translating stage comprising, a vacuum tube including asource of electrons, an anode, a control electrode, a signal-inputelectrode between said control electrode and said anode efiective tocontrol the electron stream from said source to said anode and having agreater efiect on the electron stream over one cross-sectional portionof the electron path than on that over another'portion, and an auxiliarycontrol electrode efiective to control the electron stream from saidsource tov said anode and having a greater effect on the electron streamover said other portion than on that over said one vacuum tube includinga source of electrons, an anode, a control electrode, and a signal-inputelectrode between said control electrode and said anode eifective tocontrol the electron stream from said source to said anode and having agreater effect on the electron stream over one cross-sectional portionof'the electron path than on that over another portion so that normallythe transconductance from said signal-input electrode to said anode isprimarily determined by the control of the electron stream through saidone portion, and means for applying a variable negative potential tosaid control electrode for increasing the ratio of the average densityof the electron stream over said other of said portions to that oversaid one of said portions,

whereby the portion of said transconductance determined by the electronstream through said other of said portions is materially increased.

9. In a modulated-carrier signal receiver including an antenna and asignal-translating channel, a first signal-translating stage in saidportion, said stage including means incidentally coupling saidsignal-input electrode and said auxiliary electrode and including theinterelectrode capacitance between said electrodes so that normally thetransconductance from said signalinput electrode to said anode isprimarily determined by the control of the electron stream through saidone portion, and means for applying a unidirectional potential to saidcontrol electrode for increasing the ratio of the average density of theelectron stream over said other of said portions tothat over said one ofsaid portions. whereby the portion of said transconductance determinedby the electron stream through said other of said portions is materiallyincreased.

'7. A signal-translating stage comprising, a vacuum tube including meansfor forming a virtual cathode, an anode, and a signal-input electrodeefiective to control the electron stream from said virtual cathode tosaid anode and having a greater efiect on the electron stream over onecross-sectional portion of the electron path than on that over anotherportion so that normally the transconductance from said signalinputelectrode to said anode is primarily determined by the control of theelectron stream through said one portion, and means for increasing theratio of the average density of the electron stream over saidother .ofsaid portions to that over said one of said portions, whereby theportion of said transconductance determined by the electron streamthrough said other of said portions is materially increased.

8. A signal-translating stage comprising, a

signal-translating channel comprising, a vacuum tube including a sourceof electrons, an anode, a control electrode, and a signal-inputelectrode between said control electrode and said anode effective tocontrol the electron stream from said source to said anode and having agreater efiecton the electron stream over one cross-sectional portion ofthe electron path than on that over another portion so that thetransconductancefrom said signal-input electrode to said anodeis'primarily determined by the control of the electron stream throughsaid one por'tion,'means for coupling said signal-input electrode tosaid antenna, and means for applying a unidirectional potential to saidcontrol electrode for increasing the ratio of the average density of theelectron stream over said other or said' portions to that over said oneof said portions, whereby the portion of said transconductancedetermined by the electron stream through said other of tions ismaterially increased.

10. In a modulated-carrier wave-signal receiver including an antenna, asignal-translating channel, and a source of automatic amplificationcontrol voltage, a first signal-translating stage in saidsignal-translating channel comprising, a vacuum tube including a sourceof electrons, an anode, a control electrode, and a signal-inputelectrode between said control electrode and said anode effective tocontrol the electron stream from said source to said anode and having agreater effect on the electron stream over one cross-sectional portionof the electron path than on that over another portion so that normallythe transconductance from said signal-input electrode to said anode isprimarily determined by the control of the electron stream through saidone portion, means for coupling said signal-input electrode to saidantenna, and means for applying a potential from said source ofautomatic amplification control voltage to said control electrode forincreasing the ratio of the average density of the electron stream oversaid other of said portions to that over said one of said portions,whereby the portion of said transconductance determined by the electronstream through said other of said portions is materially increased forreceived signal amplitudes of large value,

11. A signal-translating stage comprising, a vacuum tube including, inthe order named. a

said porcathode, a first electrode, a secondelectrode, a

signal-input electrode, and an anode. means for applying a positiveunidirectional operating potential to said second electrode, saidsignal-input electrode being eflective to control the electron streamfrom said source to said anode and having a greater efiect on theelectron stream over one cross-sectional portion of the electron paththan on that over another portion so that normally the transconductancefrom said signalinput electrode to said anode is primarily determined bythe control of the electron stream through said one portion, and meansfor applying a variable negative potential to said first electrode forincreasing the ratio of the average density of the electron stream oversaid other of said portions to that over said one of said portions,whereby the portion of said transconductance determined by the electronstream through said other of said portions is materially increased.

12. A signal-translating stage comprising, a

0! the average density of the electron stream over said other of saidportions to that over said one of said portions, whereby the portion ofsaid transconductance determined by the electron stream through saidother of said portions is materially increased.

15. A signal-translating stage comprising, a

control electrode including, in the order named,

a source of electrons, a signal-input electrode, a 1

screen grid, an additional electrode, and an anode, said signal-inputelectrode being effective to control the electron stream from saidsource to said anode and having a greater eifect on the electron streamover one cross-sectional portion of the electron path than on that overanother portion, means comprising said additional elecvacuum tubeincluding a source of electrons, an

trode for varying the electron stream to said anode at a preselectedfrequency, whereby the normal conversion ttansconductance from saidsignal-input electrode to said anode is primarily determinedby thecontrol of the electron stream through said one portion, and means forincreasing the ratio of the average density of the directional potentialto said control electrode for decreasing the density of the electronstream over said one portion, whereby the portion of saidtransconductance determined by the electron stream passing through saidother oi said portions is materially increased.

13. A signal-translating stage adapted to translate signal inputs withina wide amplitude range comprising, a vacuum tube including a source ofelectrons, an anode, a control electrode, and a signal-input electrodebetween said control electrode and said anode eiiective to control theelectron stream from said source to said anode and having a greaterefiect on the electron stream over one cross-sectional'portion oi theelectron path than on that over another portion so that normally thetransconductance from said signal-input electrode to said anode isprimarily determined by the control of the electron stream through saidone portion, and means responsive to the amplitude of said signal inputfor applying a unidirectional potential to said control electrode forincreasing the ratio of the average density of the electron stream oversaid other of said portions to that over said one of said portions.whereby the portion of said transconductance determined by the electronstream through said other of said portions is materially increased.

14. A signal-translating stage comprising, a vacuum tube including asource of electrons, an anode, a signal-input electrode efiective tocontrol the electron stream from said source to said anode and having agreater efiect on the electron stream over one cross-sectional portionof the electron path than on that over another portion so that normallythe conversion transconduct- .ance from said signal-input electrode tosaid anode is primarily determined by control of the electron streamthrough said one portion, an additional means for varying at apreselected frequency the electron stream from said source to saidanode, and means for increasing the ratio electron stream over saidother of said portions to that over said one of said portions, wherebythe portion of said transconductance determined by the electron streamthrough said other of said portionsis materially increased.

16. A signal-translating stage comprising, a vacuum tube including asource of electrons, an anode, and a signal-input electrode efiectivetocontrol the electron stream from said source to said anode and having agreater eiiect on the electron stream over one cross-sectional portionof the electron path than on that over another portion so that normallythe conversion transconductance iromsaid signal-input electrode to saidanode is primarily determined by the control of the electron streamthrough said one portion, means included in said vacuum tube forproviding sustained oscillations and for utilizing said oscillations tovary the electron stream to said anode, and means for increasing theratio of the average density of the electron stream over said other ofsaid portions to that over said oneoi said portions, whereby the portionof said transconductance determined by the electron stream through saidother of said portions is materially increased.

17. A signal-translating stage comprising, a vacuum tube including, inthe order named, a source of electrons, a signal-input electrode, ascreen electrode, an additional electrode, and an anode, means includingsaid additional electrode for providing sustained oscillations and forutilizing said oscillations to control the electron stream to saidanode, said signal-input electrode being effective to control theelectron stream-from said source to said anode and having a greatereffect on the electron stream over one cross-sectional portion of theelectron path than on that over another portion so that normally theconversion transconductance from said signal-input electrode to saidanode is primarily determined by the control of the electron streamthrough said one portion, and means for increasing the ratio of theaverage density of the electron stream over said other of said portionsto that over said one of said portions, whereby the portion of saidtransconductance determined by the electron ARTHUR V. LOUGHREN.

